1. Field of the Invention
This invention relates to a jaw cylinder which typically lends itself to use at the folding station of a rotary printing press for folding successive sheets of printed paper into signatures. More particularly, the invention deals with such a jaw cylinder having two or more sets of fixed and movable jaws arranged at circumferential spacings thereon for folding the printed sheets as they are thrust into the jaw cavities by folding blades on a folding cylinder which also is included in the folding mechanism. Still more particularly, the invention is directed to how to open and close the set or sets of jaws on the jaw cylinder in timed relationship to the thrusting of the successive sheets off the surface of the folding cylinder by the folding blades.
2. Description of the Prior Art
The folding mechanism for a web-fed printing press usually comprises a cutting cylinder in addition to the noted folding cylinder and jaw cylinder. The printed web of paper is first wrapped around part of the folding cylinder which is in constant rotation in the course of printing and, while being done so, cut into successive sheets by cutting blades on the cutting cylinder which is held against the folding cylinder via the web. The folding cylinder is equipped with elongate folding blades arranged at circumferential spacings thereon and each extending parallel to the axis of the folding cylinder. Each folding blade is movable radially of the folding cylinder.
Pushed in part off the surface of the folding cylinder by one of the folding blades, the sheet together with the folding blade is inserted in one of the jaw cavities formed in the surface of the jaw cylinder at circumferential spacings, the jaw cylinder being in rolling engagement with the folding cylinder. The sheet thus pushed into the jaw cavity is therein engaged between the fixed and the movable jaws as the movable jaw is closed against the fixed jaw, and thereby folded in the middle. The thus folded sheet is subsequently carried away from the surface of the folding cylinder by the jaw cylinder.
It is therefore apparent that each movable jaw on the jaw cylinder must be closed against the fixed jaw to grip the sheet therebetween in split-second precision timing to the thrusting of this sheet into the cavity between the jaws by one associated folding blade on the folding cylinder. Should this timing be improper, the sheets would not be captured by the jaws but might be ruined or smeared by rubbing against the folding blades or the jaws, resulting in a drop in the rate of production or in the quality of the printings. The folding blades and the jaws might also go out of order and wear out prematurely.
For pivotal motion into and out of sheet-folding engagement with the fixed jaw, the movable jaw is mounted to a jaw carrier shaft which in turn is mounted to the jaw cylinder in parallel spaced relationship to the jaw cylinder axis. The jaw carrier shaft has cam follower means on one end thereof for engagement with a jaw drive cam of annular or disklike shape on the frame means. As the jaw cylinder rotates, the jaw carrier shaft revolves with the cam follower means in constant engagement with the jaw drive cam, thereby to be rotated bidirectionally about its own axis and hence to cause the movable jaw to pivot into and out of sheet-folding engagement with the fixed jaw.
Thus the jaw drive cam must be in exact angular position relative to the jaw cylinder in order to cause the pivotal motion of the movable jaw in proper timing to the thrusting motion of the associated folding blade on the folding cylinder. Furthermore, even if the jaw drive cam is initially correctly positioned relative to the jaw cylinder, readjustment may become necessary in course of time because of change in the timing as a result of the wear of the jaws and the folding blades.
The concept of making the jaws of the jaw cylinder adjustable in timing to the folding blades on the folding cylinder is itself not new in the art. Japanese Unexamined Utility Model Publication Nos. 4-22463 and 5-26949 are hereby cited as teaching jaw cylinders complete with timing mechanisms for the jaws.
The jaw cylinder according to the first cited reference has two sets of fixed and movable jaws in circumferentially spaced positions thereon. The movable jaws of the two jaw sets are pivotally mounted one to each of two jaw carrier shafts which in turn are rotatably mounted to the jaw cylinder in diametrically opposite positions thereon and which extend parallel to the jaw cylinder axis. These two jaw carrier shafts have cam follower means each on one end thereof for constant engagement respectively with the peripheries of two jaw drive cams of annular or disklike shape mounted to the frame means. The two jaw drive cams are displaced from each other axially of the jaw cylinder. One of them is angularly displaceable relative to the frame means about the axis of the jaw cylinder. The angular position of this one cam is adjustably variable from outside the frame means by turning a drive pinion in mesh with a driven gear rotatable with that cam, in order to adjust the opening and closing of one associated set of jaws to the thrusting motion of one associated folding blade on the folding cylinder.
The second mentioned reference, Japanese Unexamined Utility Model Publication No. 5-26949, suggests a jaw cylinder that is similar to that of the first citation in having two sets of fixed and movable jaws, with the movable jaw of each set pivotally mounted on one of two jaw carrier shafts. These jaw carrier shafts have cam follower means in constant engagement respectively with the peripheries of two jaw drive cams mounted to the pair of confronting framing walls between which is supported the jaw cylinder. Here again, only one of the jaw drive cams is angularly displaceable about the jaw cylinder axis by gear drive similar to that of the first described prior art.
Thus the two Japanese utility model applications cited above are alike in that only one of the two sets of jaws is readjustable by varying the angular position of one associated jaw drive cam. The other, non-readjustable jaw drive cam must be mounted in an angular position that has been determined as a result of careful observation of how the opening and closing of the set of jaws is timed to the thrusting motion of one associated folding blade on the folding cylinder. Skilled labor as well as an expenditure of unjustifiably long time has therefore been required for mounting the non-readjustable jaw drive cam at the time of assemblage, maintenance, and repair, adding substantively to the installation and running cost of the printing press. What is more, not even the slightest readjustment has been possible during the progress of printing, without setting the complete machinery out of operation.
The gear drive employed by both prior art devices for readjustment of one set of jaws is itself objectionable. The need arises in practice for turning the jaw drive cam through as small an angle as, say, a tenth degree for precisely timing the jaws to the folding blade. An inordinately fine turn of the drive pinion is required for turning the jaw drive cam through such a small angle. Aggravating the difficulty of such fine readjustment is the backlash inherent in the gearing, which is too great compared to the required angle of turn of the drive pinion. Such readjustment has indeed been possible only by highly skilled personnel, and that with trials and errors.